1. Field of the Invention
The present invention relates to a reel lock mechanism for use in a tape cassette, and more particularly to a reel lock mechanism capable of reliably preventing a tape from becoming loose or slacked in a tape cassette.
2. Description of the Prior Art
Magnetic tape cassettes for use in video tape recorders (VTRs) or the like have a reel lock mechanism for preventing the magnetic tape from becoming loose or slacked when not in use.
FIG. 7 of the accompanying drawings shows one such reel lock mechanism a.
As shown in FIG. 7, a lower tape cassette member b supports a pair of tape supply and takeup reels with a magnetic tape d wound thereon, the tape supply and takeup reels having respective lower flanges c, c'. The lower flanges c, c' have series of teeth e, e', respectively, on their outer circumferential edges.
The reel lock mechanism a, which is incorporated in the lower tape cassette member b, has a reel lock assembly f positioned substantially between the tape supply and takeup reels. The reel lock assembly f comprises a main body g and a pair of lock fingers h, h' projecting from the main body g. The reel lock assembly f is normally urged in the direction indicated by the arrow A by a spring (not shown).
The lock fingers h, h' are made of a resilient material. The reel lock assembly f is urged in the direction A to keep the lock fingers h, h' in engagement with the respective teeth e, e' to lock the tape supply and takeup reels against rotation in one direction. More specifically, the lock fingers h, h' allow the flanges c, c' to rotate in the respective directions indicated by the arrows B, B', i.e., in the directions to keep the magnetic tape d under tension, but prevent the flanges c, c' from rotating in the opposite directions to cause the magnetic tape d to become loose or slacked.
When a force indicated by the arrow F in FIG. 8 of the accompanying drawings is applied to the supply reel flange c due to vibration or the like, the reel lock assembly f is displaced in the direction indicated by the arrow C, bringing the lock finger h' out of engagement with the teeth e' of the takeup reel flange c'. Since the tape takeup reel can now rotate in the direction to permit the magnetic tape d to become loose, the magnetic tape d tends to be loosened or slacked, and can possibly be jammed in the tape cassette.
One solution is to employ a pair of lock fingers i, i' having respective notches j, j', as shown in FIG. 9 of the accompanying drawings. When the force F is imposed on the supply reel flange c, the lock finger i is bent at the notch j, releasing the force F. Therefore, the reel lock assembly f is not displaced, and the lock finger i' remains in engagement with the teeth e' of the takeup reel flange c'. However, since the notches j, j' make the lock fingers i, i' mechanically weak, the lock fingers i, i' may be forcibly bent out of engagement with the teeth e, e' depending on the magnitude of the force applied to the tape supply and takeup reels.
As shown in FIG. 10 of the accompanying drawings, an unlock arm m is inserted through a hole 1 defined in a bottom wall k of the lower tape cassette member b. When the unlock arm m is inserted into the main body g and engages and laterally pushes a cam surface n of the main body g, the reel lock assembly f is displaced to unlock the lock fingers h, h' from the respective teeth e, e'. The greater the distance that the reel lock assembly f is displaced, the more reliably the lock fingers h, h' can be locked on and unlocked from the respective teeth e, e'. The distance that the reel lock assembly f is displaced may be increased by increasing the stroke that the unlock arm m is inserted into the main body g. However, an increase in the stroke of insertion of the unlock arm m into the main body g results in an increase in the distance that the magnetic tape cassette has to move when it is loaded into a video tape recorder. Another way of increasing the distance that the reel lock assembly f is displaced is to increase the angle by which the cam surface n is inclined. This attempt is not preferable as it will cause the cam surface n to be scraped off when the cam surface n is repeatedly engaged by the unlock arm m.